In a multi-cavity injection molding apparatus having a hot runner manifold for delivering a melt stream of moldable material to a plurality of hot runner nozzles, the heat distribution throughout the manifold is typically uneven. This uneven heat distribution causes the manifold to warp. As a result, the distance between the lower surface of the manifold and each of a plurality of mold cavities varies and thus each nozzle is subjected to unique operating conditions depending on the nozzle's location relative to the manifold. As such, the thermal expansion results in a variable sealing force being applied to both the interface between the nozzle and manifold and the nozzle and mold gate. If the manifold “floats” where a head of the nozzle is in contact with the lower surface of the manifold but not attached to it, an uneven sealing condition may allow the pressurized melt to leak at the interface between the manifold and each nozzle and/or in the mold gate area around the nozzle seals. If the nozzles are threaded into the manifold, an uneven sealing condition may still allow the pressurized melt to leak in the mold gate area.
Edge gating from a nozzle of an injection molding apparatus through a number of edge gate seals is well known. A multi-cavity edge, or side, gated injection molding apparatus 100 is shown in FIG. 1 that is described in U.S. Pat. No. 5,494,433 to Gellert, issued Feb. 27, 1996, which is incorporated by reference herein in its entirety. Generally, the multi-cavity edge-gated injection molding apparatus 100 includes several nozzles 102, one of which is shown in FIG. 1, that are coupled to a hot runner manifold 118 to receive a melt stream of moldable material therefrom.
Each nozzle 102 is mounted in an opening 104 in a mold plate 106. Nozzle 102 includes a nozzle melt channel 108 for receiving the melt stream from a manifold melt channel 132 and delivering the melt stream to mold cavities 112 via mold gates 110. Nozzle 102 includes a nozzle heater 126 that is monitored and controlled by a thermocouple 128, and manifold 118 includes a manifold heater 130. Nozzle heater 126 and manifold heater 130 are provided to maintain the melt stream of moldable material within melt channels 108, 132, respectively, at a proper processing temperature.
Mold cavities 112 are formed between respective cavity inserts 154 and mold cores 156. Cavity insert 154 is disposed within mold plate 106 and includes seals 150 and cooling channels 152 there between. Each mold core 156 is held in place by a mold insert 158. Mold cavities 112 are radially spaced around nozzle 102 with each mold gate 110 extending through a gate insert 114 that is held in position by a gate insert retainer plate 122 and mold insert 158. Each mold gate 110 is aligned with a gate seal 116 that is threadably coupled to a downstream end of nozzle 102. As such, the location of gate seals 116 is generally fixed relative to mold plate 106.
As illustrated in FIG. 1, manifold 118 is a “floating” manifold that is positioned below a back plate 120 and coupled to nozzle 102 such that manifold 118 does not contact mold plate 105. This arrangement allows for thermal expansion of manifold 118 and nozzle 102 in an axial direction. In such an arrangement, requisite axial thermal expansion of manifold 118 is accommodated by having a sliding/telescopic arrangement between manifold 118 and a sprue bushing 124 fixed to back plate 120. However, axial thermal expansion of nozzle 102 is restricted in a direction of mold cavities 112 by the relatively fixed position of gate seals 116. Consequently, gate seals 116 may bear the load of both manifold 118 and edge-gating nozzle 102 during operation of injection molding apparatus 100. Due to the strenuous and repetitive nature of the injection molding process, such a load condition may cause misalignment of gate seals 116 with their respective mold gates 110 and/or excessive wear of gate seals 116 resulting in leakage and more frequent repair and maintenance.
What is needed is an improved connection between a hot runner manifold and a nozzle that accommodates thermal expansion of the nozzle and some deflection of the manifold without causing a variable or excessive force being applied between the nozzle and the manifold or the nozzle and a mold gate of an injection molding system.